The production of cycloalkylaromatic compounds, such as cyclohexylbenzene, is a commercially important process since the latter has utility as a solvent and a source of chemical intermediates, such as, for example, phenol and cyclohexanone, which are important intermediates in the production of, for example, phenolic resins, bisphenol A, ε-caprolactam, adipic acid and plasticizers.
One process for producing cycloalkylaromatic compounds, such as cyclohexylbenzene, involves the catalytic hydroalkylation of aromatic compounds, such as benzene, over a bifunctional catalyst. The bifunctional catalyst may comprise an alkylation component comprising a solid acid, such as a molecular sieve, or amorphous silica-alumina, or any suitable solid acid, and a hydrogenation component, such as a Group 8-10 metal. The hydrogenation component may be introduced into the catalyst by impregnation with a solution of a water-soluble salt of the relevant Groups 8-10 metal. The catalyst may also comprise promoters, such as, for example, alkali or alkali-earth metals, Group 3 or Group 4 metals, Zn, Sn, Re, halogens, etc. The impregnated catalyst is then dried and calcined in air, typically at a temperature of 250° C. to 550° C. To bring the catalyst into its active form, the catalyst is then heated in the presence of hydrogen primarily to reduce the hydrogenation component to its active metallic form. This activation process may also serve to remove adsorbed water that would inhibit the alkylation reaction.
An example of such a process is described in, for example, U.S. Pat. No. 3,760,017, which discloses a method for the catalytic hydroalkylation of benzene to cyclohexylbenzene using a bifunctional catalyst followed by the conversion of the cyclohexylbenzene to cyclohexanone and phenol by air oxidation and acid decomposition. The bifunctional catalyst comprises a metal in Groups 8-10 of the Periodic Table selected from the group consisting of cobalt, nickel and palladium and an acidic oxide support consisting essentially of a substantially alkali metal-free mixture of about 5 to 60 percent by weight of a crystalline zeolite, such as zeolite Y, and about 95 to 40 percent by weight of a silica-alumina cracking catalyst. The bifunctional catalyst is produced by impregnating the support with a solution of the desired hydrogenation metal(s) followed by calcining in an oxidizing atmosphere to convert the hydrogenating component to the oxide form. The catalyst is then reduced, by contact with hydrogen at a temperature of 400° F. to 1200° F. (204° C. to 649° C.).
A further process for the catalytic hydroalkylation of benzene is described in U.S. Pat. No. 6,037,513, in which the bifunctional catalyst comprises a crystalline inorganic oxide material having alkylation activity and an X-ray diffraction pattern including d-spacing maxima at 12.4±0.25, 6.9±0.15, 3.57±0.07, and 3.42±0.07 Angstrom and a hydrogenation metal selected from palladium, ruthenium, nickel, and cobalt. In the Examples, the catalyst is produced by impregnating the crystalline inorganic oxide material with an aqueous solution of a metal salt and then treating the impregnated oxide material with 50 cc/min of flowing hydrogen for 2 hours at 300° C. and 1 atm pressure. Although not stated in the '513 patent, this hydrogen treatment activates the catalyst by reducing the metal salt to its elemental form.
In WO 2012/050751, a process of the hydrogen activation of a catalyst is conducted at a temperature below 250° C., such as at temperature in a range from 0 to 200° C. Lowering the activation temperature is found to increase the cyclohexylbenzene selectivity of the catalyst. In the Examples, the catalyst is produced by impregnating the bound crystalline inorganic oxide material with an aqueous solution of palladium chloride and then activating the impregnated oxide material in the hydroalkylation reactor with a flow of 47-80 microliter/min benzene and 15-25 sccm hydrogen while the reactor temperature is ramped to 145° C. at 1° C./minute. In some cases, the hydrogen activation is preceded by a drying step where the catalyst is heated at a temperature below 200° C., in the presence of a dry gas, such as nitrogen, to reduce the water level of the catalyst to less than 15 wt %, such as 1 wt % to 12 wt %.